Lanthanide-Enabled Lattice Engineering of Copper(I) Cluster Scintillators

Copper(I) clusters are attractive scintillators, yet their intrinsic dual-band emission from competing metal/halide-to-ligand charge-transfer (3MXLCT) and cluster-centered (3CC) states partitions excitation energy between distinct emissive pathways. Here, we report a molecular lattice-engineering strategy that regulates this excited-state competition through trivalent lanthanide (Ln3+) incorporation. Heterometallic Cu-Ln coordination networks constrain ligand relaxation, thereby suppressing 3MXLCT emission while preserving cluster-centered emission to produce single-band scintillation. Systematic comparison of (NHIC)6(DMF)2Ln2Cu4I4 (Cu-Ln-NHIC; Ln = La, Eu, Gd, Ho, Lu) reveals that efficient 3CC emission depends on both the local coordination environment surrounding the Cu4I4 cluster and the electronic structure of the Ln3+ ion. La3+ provides a relatively less confined Cu4I4 environment, while its 4f0 configuration avoids competing lanthanide-centered excited states, resulting in a photoluminescence quantum yield of 90% and a scintillation light yield of 16,015 photons MeV-1, corresponding to a 117-fold enhancement in radioluminescence intensity relative to Cu-NHIC. Cu-La-NHIC further achieves an X-ray detection limit of 12.5 nGy s-1 and a spatial resolution of 22.3 lp mm-1. These results establish lattice regulation of competing excited-state pathways as a molecular design principle for single-band, efficient Cu(I)-cluster scintillation.